This invention relates to image displays, and more particularly to methods of augmenting white light filtered through a color wheel, or colored lamp light, and used to illuminate the display.
Spatial light modulators (SLMs) have found application in many fields, a significant one of which is image displays. In general, an SLM is an array of light-emitting, light-transmitting, or light-reflecting elements, which are individually addressable, usually with electronic signals. Many SLMs are binary, having an addressing scheme that switches its elements to either an xe2x80x9conxe2x80x9d or xe2x80x9coffxe2x80x9d state to form the image. A characteristic of SLMs is that there is no scanningxe2x80x94all pixels are activated at substantially the same time to generate the entire image or a two-dimensional block of the image, depending on the size of the image and the SLM.
One type of SLM is a digital micro-mirror device (DMD), also known as the digital light processor (DLP), manufactured by Texas Instruments Incorporated. The DMD has an array of thousands of tiny tilting mirrors. To permit the mirrors to tilt, each is attached to one or more hinges mounted on support posts and each is spaced by means of an air gap over underlying addressing circuitry. The addressing circuitry provides electrostatic forces, which cause each mirror to selectively tilt.
For display applications, the DMD is addressed with image data. In accordance with this image data, light is selectively reflected either into a projection pupil or into a xe2x80x9cdumpxe2x80x9d. The combination of light and dark mirrors projected onto a viewing screen forms an image. Modulation techniques are used to provide greyscale image xe2x80x9cframesxe2x80x9d. A quick succession of frames is perceived by the viewer as a full motion display.
There are at least two approaches to generating color displays with the DMD display system. One approach is to generate multiple images with multiple SLMs, typically one SLM each for red, green and blue. Each image has a desired intensity, and the images are combined to result in the correctly colored display. A second approach is to use a single SLM and generate images for each color (red, green, and blue) sequentially. A white light source is filtered through a revolving color wheel, such that a desired color illuminates the corresponding image. The differently colored images are generated so quickly that the eye integrates them into the correctly colored frame.
An issue with lamps used in display systems is that they tend to be deficient in the red spectrum of the visible light region. This limits the number of lumens that can be projected onto a viewing screen while maintaining esthetically pleasing color balance.
One aspect of the invention is an illumination system for a spatial light modulator that is illuminated with light from a color wheel and sequentially displays differently colored images. In one embodiment, the solid state light source is xe2x80x9cforwardxe2x80x9d of the color wheel, relative to a white light source. The white light source, such as a lamp, provides white light in the visible spectrum. A solid state light source augments the white light by providing light in a desired spectral region. A beam combiner overlays the light from the white light source with the light from the solid state light source. This combined beam is focused through the color wheel, which has multiple color segments for filtering the light. Various timing alternatives may be implemented such that the augmentation is during the complete revolution of the color wheel or only during part of each revolution. Various lens and mirrors may be used to focus the light from the white light source and the light from the solid state light source along an optical path to the spatial light modulator.
In other embodiments, the solid state light source may be xe2x80x9cbehindxe2x80x9d the color wheel. Also, in each embodiment, multiple solid state light sources could be used to augment different colors.
An advantage of the invention is that it can be used to provide good color balance in displays generated with a color wheel display system. For example, solid state illumination can be used to augment red lamp illumination without throwing away blue and green lamp illumination. Additionally, a solid state source can be used to compensate light loss during transitions between segments of the color wheel. In sum, the solid state source enhances picture quality, without adding undue expense or complexity to the display system.
The high switching speeds and longevity of solid state sources make them a good supplement to any lamp source in an SLM display system, whether the lamp be a white light lamp in a color wheel system (sequential colored images) or a color lamp in a multiple SLM (concurrent colored images) system.